This invention relates to a type of valve known as a “backflow preventer check valve.” These types of check valves are well known and are widely used to control backflow of fluids carrying undesirable contaminants into a fluid supply. These valves have evolved to become highly specialized in their function and operation, and are similar in that they all contain spring-loaded members which are biased towards the valve-closed position until fluid pressure acting on the checking members forces the valves open. Although the invention of the present application may be used in any suitable environment in which the flow of liquids must be controlled, the invention is preferably intended for use on a backflow preventer, which is a well-known device commonly used to protect potable water supplies from pollutants originating from downstream sources.
Many prior art spring-loaded check valves are of a poppet type, and include checking members whose movement is linear and remain in the fluid path. The pressure required to open such check valves is established by regulation and provides a minimum degree of protection against reverse flow. To provide some degree of protection, the springs in spring-loaded check valves provide a static differential pressure drop and corresponding static energy while the check valves are in a closed, or “no flow,” condition. The pressure and corresponding energy required to open these check valves is provided by the fluid and is created at the source by, for example, a pump. As fluid flows through the valve, both the differential pressure drop and corresponding energy change from static to dynamic. The total dynamic energy of the fluid in motion through the check valves is reduced by friction within the pipes and other obstacles (including the checking members) which remain disposed directly in the fluid path within the fluid conduit system. Once it increases beyond a certain amount, this loss of dynamic energy, also known as “headloss,” is no longer beneficial. Due to the position and linear movement of the springs within typical spring-loaded check valves, as headloss increases, fluid pressure decreases. This results in reduced fluid flow.
Applicant's prior U.S. Pat. No. 6,443,184 provides significant improvement in the operation of radial-loaded poppet-type valves by providing a plurality of springs pivotally mounted in the interior of the valve housing and interconnecting the valve housing and stem for normally maintaining the seal retainer in sealing engagement with the valve seat in the absence of fluid flow. The springs are positioned in a radial position and extend outwardly from the stem towards the edge of the seal retainer to cause the seal retainer to move away from the valve seat in response to fluid flow in the downstream direction. This movement thereby increases the force of the stem on the springs and causes the springs to pivot and compress to produce a diminishing resultant spring load on the stem. This valve provides the required axial load when the poppet is in the closed, no-flow condition. However, as flow commences, the axial load dimimishes and approaches zero. Some embodiments, such as tubes with small orifices will benefit if the load diminishes and the poppet stroke is extended to allow a smoother flow path.
The invention of the present application provides a further advantageous function by allowing the poppet to have an extended stroke past the neutral position, thus enhancing the flow characteristics of the valve.